My previous U.S. Pat. No. 5,297,450, entitled Positive Variable Drive Transmission, discloses a novel transmission having a relatively simple and reliable construction. The transmission includes two parallel drive shafts that mount a series of gear pairs of progressively varying gear ratio. A series of overrunning clutches are interposed between one of the gear members of each pair and one of the drive shafts for interconnecting the two shafts at any one of the gear ratios.
Externally controlled actuators index the overrunning clutches between two limit positions, neither of which entirely deactivates the clutches. One of the limit positions enables the engagement of the overrunning clutches in response to one direction of relative rotation between the gear members and their mounting shaft, and the other limit position enables the engagement of the overrunning clutches in response to the opposite direction of relative rotation. The two opposite directions of relative rotation correspond to (a) the transmission of forward drive power between a vehicle's engine and its drive wheels and (b) the transmission of forward braking power in which the engine is used to slow forward momentum of the vehicle.
The overrunning clutches can be two-way roller clutches. A cam disk having a plurality of recesses in its peripheral surface is connected to one of the drive shafts, and a roller retainer supports a plurality of rollers within the recesses. A bearing race formed in respective hubs of the gear members surrounds the cam disk and roller retainer. The two limit positions are defined in part by opposing ramp surfaces at opposite ends of the recesses in the cam disk. The roller retainer is indexable between the two limit positions at which the rollers are wedged between one of the opposing ramp surfaces and the bearing race.
The externally controlled actuators can be hydraulically operated indexing mechanisms that include stationary housings having pairs of supply ducts for discharging fluid along predetermined trajectories. Annular plates having circumferentially spaced vanes are attached to opposite sides of the roller retainers. The vanes are positioned in communication with the supply ducts so that the fluid discharged from the supply ducts causes the roller retainers to rotate with respect to the cam disks. Separate ducts are provided for rotating the roller retainers in opposite directions between the two limit positions.
A computer can be used to control the indexing mechanisms to successively engage the roller clutches of progressive gear ratios at one or the other limit positions for "up shifting" or "down shifting" the transmission. For example, the roller clutches are successively indexed to one limit position for "up shifting" the transmission, and successively indexed to the other limit position for "down shifting" the transmission. The engagement of succeeding gear ratios, while "up shifting" or "down shifting", causes a reversal of relative rotation between the gear members and the drive shaft of all succeeded gear ratios.
Accordingly, the succeeded gear ratios must remain at the same limit position as the engaged gear ratio to prevent the two drive shafts of the transmission from being connected at two different gear ratios. An interlocking system of pins and slots connecting adjacent roller retainers maintains all of the succeeded roller clutches in the same limit position. The transmission can be shifted out of sequence; however, any succeeded gear ratio that is skipped is indexed together with the just engaged gear ratio to the same limit position.